Aging skin is the result of more than just chronological age. Skin is exposed to various environmental stresses, such as UV rays, which cause free radicals to form in the skin. Free radicals include, for example, singlet oxygen, hydroxyl radical, the superoxide anion, nitric oxide and hydrogen radicals. Free radicals attack DNA, membrane lipids and proteins, generating carbon radicals. These in turn react with oxygen to produce a peroxyl radical which may attack adjacent fatty acids to generate new carbon radicals. This process can lead to a chain reaction producing lipid peroxidation products. Damage to the cell membrane can result in loss of cell permeability, increased intercellular ionic concentration and/or decreased ability to excrete or detoxify waste products. The end result is a loss of elasticity of the skin and the appearance of wrinkles leading to premature ageing of the skin. This process is commonly referred to as photo-aging.
Thus, it is an object of the present invention to provide a composition and process for protecting cellular targets from aging and photo-damage caused by UV light, in general, and free radicals formed thereby, in particular.
The degree of UV protection afforded by a composition is directly related to the amount and type of sunscreen actives present therein. The more sunscreen actives present, the greater the degree of UV protection. However, in order to incorporate significant amounts of sunscreen actives into a composition, a large amount of emulsifiers have also needed to be used in order to make the composition stable so as to avoid separation and precipitation of ingredients. The use of significant amounts of emulsifiers, while making the composition more stable, detracts from the texture and feel of the composition when applied onto a keratinous substrate.
Thus, it is yet another object of the present invention to provide a sunscreen composition which provides a significant degree of UV protection, is stable, while at the same time having a light, non-oily texture and skin feel property.
Lastly, conventional sunscreen compositions are expected to possess water-resistance properties in order to inhibit the protective composition from being easily removed from a keratinous substrate surface by sweat and exposure to water. In order to achieve this function, film-formers are typically employed in the composition. By forming a film on the keratinous substrate surface, the sunscreen actives are more steadfastly held in place upon exposure to water. The use of film-formers, however, has a negative impact of the tactile properties of the composition, rendering it more tacky feeling.
Thus, it is another object of the present invention to provide a sunscreen composition which possesses water-resistance properties but does not require the use of a film-former.